Zinc enriched lithium silicate-latex coating composition

ABSTRACT

A zinc-enriched protective coating comprises a vehicle containing an alkali-lithium silicate solution with sufficient alkali silicate, preferably lithium, to provide a self-curing one-coat composition, an organic interpolymer latex to provide improved adhesion, and zinc dust to provide cathodic protection.

CROSS REFERENCE TO RELATED APPLICATION

This is a division, of application Ser. No. 319,969, filed 12/29/72, nowU.S. Pat. No. 3,884,863.

This application is a continuation-in-part of Ser. No. 93,389, filedNov. 27, 1970 now abandoned, which is a continuation of Ser. No. 708,785filed Feb. 28, 1968, now abandoned in the names of Ronald W. Beers andJulian Lakritz, entitled "Zinc Enriched Lithium Silicate-Latex CoatingComposition."

BACKGROUND OF THE INVENTION

The present invention is directed to a vehicle comprising an alkalisilicate solution and an organic interpolymer latex and coatingstherefrom, which possess unusual adhesion to any type of substratecommonly encountered in coating applications. The vehicles of thepresent invention have excellent package stability and film formingproperties, and the coating compositions made by pigmenting with highloadings of zinc dust impart the same excellent corrosion resistanceassociated with the prior art zinc-rich inorganic coatings.

Heretofore, the prior art zinc-rich inorganic coatings had poor adhesionto metallic substrates unless the surface was properly prepared bysandblasting the surface free of all contaminants, such as, rust andmill scale. Such prior art zinc-rich inorganic coatings are illustratedby U.S. Pat. Nos. 3,180,746 and 3,130,061. Other prior art consideredwith respect to the present invention is represented by the followinglisted U.S. Pat. Nos.: 2,476,967, 2,767,153, 2,795,564, 2,897,182,2,980,652, 3,231,535, 3,231,537, 3,261,796, 3,261,797, and 3,261,799.

SUMMARY OF THE INVENTION

The present invention discloses a new composition for a zinc-enrichedcoating which comprises an alkali-silicate solution and an organicinterpolymer latex, the latex preferably stabilized with analkali-stable anionic surfactant. The alkali-silicate solution ispreferably a mixture of sodium and lithium silicate in amountssufficient to provide a molar ratio of sodium oxide to lithium oxide tosilicon dioxide, respectively, within the range from about 0 to 0.7 Na₂O : 0.3 to 1.0 Li₂ O : 2.5 to 4.5 SiO₂. Instead of the sodium silicateas the specific alkali silicate in the alkali-lithium silicate solution,potassium, or quaternary ammonium silicates or mixtures thereof may beused. It is preferred but not essential that lithium silicate beincluded in the composition as one of the silicates. Lithium silicate isespecially useful as a component of the solution when high waterresistance is desired. The vehicles of the present invention are suitedfor pigmentation with high loadings of zinc dust which produce asingle-application zinc-enriched coating composition with excellentadhesion and protection against corrosion of the substrates.

The coating compositions of the present invention are usually packagedas two component systems. The zinc dust and any other solid pigment usedin the coating composition is packaged as one component. The vehicle ofthe present invention together with any liquid additives is packaged asa second component. The two components are mixed prior to theapplication of the mixture to the desired surface. It has been found,according to the present invention, that less surface preparation isrequired than when prior-art zinc-rich inorganic coatings are used.Further, the coating compositions of the present invention become waterinsensitive within a short period of time and do not require the use ofa curing agent. However, curing agents such as phosphoric acid may beused to accelerate the cure when adverse conditions are encountered, andinhibitors such as chromates may be added to the composition. Curingagents are preferred for compositions that do not contain a lithium orquaternary ammonium component.

DETAILED DESCRIPTION

The vehicle component of the present invention comprises an aqueousalkali-silicate solution and an organic interpolymer latex. The aqueousalkali-silicate solution portion of the vehicle is made so as to containpreferably a mixture of sodium and lithium silicates in amountssufficient to provide a molar ratio of sodium oxide to lithium oxide tosilicon dioxide, respectively, within the range from about 0 to 0.7 Na₂O : 0.3 to 1.0 Li₂ O : 2.5 to 4.5 SiO₂. A preferred molar ratio ofsodium oxide to lithium oxide to silicon dioxide, respectively, iswithin the range from about 0.25 to 0.65 Na₂ O : 0.35 to 0.75 Li₂ O :2.5 to 4.5 SiO₂. The alkali is preferably sodium and lithium in thealkali mixture; however, any Group 1A metal silicate or quaternaryammonium silicates, or mixtures in any combination, may be used in theformulations of the invention. The quaternary ammonium compound shouldbe nonhygroscopic and water soluble.

Typical formulations of the alkali-lithium silicate solution, organicinterpolymer latex and anionic surfactant are given below:

    ______________________________________                                                         Parts by Wt. of Solids                                       ______________________________________                                        Alkali-lithium silicate sol'n.                                                                   91      69.0     57                                        Interpolymer latex 9       29.5     40                                        Anionic Surfactant 0       1.5      3                                                            100     100.0    100                                       ______________________________________                                    

As noted above, the formulations are based on weight of solids.Formulations having the best properties as to adhesion and corrosioncontain about 15 to 30 parts by weight of solids of the interpolymerlatex. The total solids of the silicate solutions is measured by heatinga weighed quantity of the silicate solution at 110° C. for 2 hours andthen weighing to determine the percent of solids. The total solids ofthe organic interpolymer latexes, on the other hand, are determind byheating at 105° C. for only 30 minutes.

The alkali-lithium silicate solutions of the present invention may beobtained by the addition of a sodium silicate solution to asodium-lithium silicate solution having a molar ratio of 0.25 Na₂ O :0.75 Li₂ O : 4.5 SiO₂ made in accordance with the disclosure of U.S.Pat. No. 3,180,746 and having a solids content of 25 to 30 percent byweight and a viscosity of between 30 to about 40 centipoises (77° F.).Sodium silicate solutions having molar ratios of Na₂ O : SiO₂ of between1 : 2.4 to about 1 : 3.75 may be added to the foregoing describedsodium-lithium silicate solution to produce the alkali-lithium silicatesolutions of the present invention. It is to be understood, however,that the alkali-lithium silicate solutions may also be produced directlyby the method disclosed in U.S. Pat. No. 3,180,746 by adjusting theamounts of lithium hydroxide, and sodium, potassium or quaternaryammonium hydroxide added to the silica-containing materials such assilicic acid or silica gel before heating.

Furthermore, the alkali-lithium silicate solutions may be obtained bythe addition of lithium hydroxide and sodium, potassium or quaternaryammonium hydroxide to alkali stabilized colloidal silica solutions. Thealkali stabilized colloidal silicas are marketed under the tradenames"Ludox" by E. I. duPont de Nemours, "Syton" by Monsanto Chemical Companyand "Nalcoag" by National Aluminate Company.

According to the present invention, it has been found that the additionof an organic interpolymer latex together with an alkali silicatesolution provides a vehicle which has unusual adhesion to substratescommonly encountered in coating applications. The organic interpolymerlatexes used in the present invention may be known alkali-stablepolymers of copolymerizable vinyl compounds which form interpolymerscapable of being cast to form films from aqueous solutions. The term"latex" designates an aqueous dispersion of the interpolymer which ispresent in the form of very fine particles.

Illustrative of the organic interpolymers which are used in the latexesof the present invention are the polyacrylates which are mixtures ofmonovinylidene esters, the monovinylidene carboxylic acids, or mixturesof esters and acids. Since the monomers when polymerized by themselvesyield either soft or brittle polymers which do not have the desired filmforming properties, a mixture of the monomers is used to form thedesired interpolymers. Typical ester monomers which are used aremethylacrylate, methylmethacrylate, ethylacrylate, ethylmethacrylate,propyl acrylate, propyl methacrylate, isopropyl acrylate, butylacrylate, isobutyl acrylate, butyl methacrylate, tert-butyl acrylate,amyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate,hexyl methacrylate, octyl methacrylate or other primary, secondary ortertiary alkyl having 2 to 18 carbon atoms, acrylates, or methacrylates,or alkoxyalkyl acrylates or methacrylates such as butoxy ethyl acrylateor methacrylate, etc. The acid monomers are preferably methacrylic oracrylic acid but other acids having vinyl groups such as itaconic,fumaric, maleic, acid or the salts of the acids may be used. Further,the "acrylates," meaning interpolymers made predominantly of theforegoing monomer, may be modified by using acrylonitrile ormethacrylonitrile, vinylacetate, a vinyl halide such as vinyl chloride,a vinyl aromatic such as styrene and the like which co-polymerize withthe monovinylidene ester and acid monomers. Specific interpolymers ofthe acrylate-type are disclosed in U.S. Pat. No. 2,795,564.

Other organic interpolymers which may be used in the latexes of thepresent invention are interpolymers of diolefins and vinyl compoundssuch as vinyl aromatic compounds, acrylonitrile, vinyl halides and theacrylates. The diolefin is preferably butadiene but isoprene andsubstituted butadiene such as 2,3-dimethylbutadiene-1,3 may also beused. The preferred vinyl aromatic compound is styrene; however, loweralkyl substituted styrene and vinyl naphthaline, etc. may be used suchas disclosed in U.S. Pat. No. 2,767,153. Interpolymers such asstyrene/butadiene/maleic acid may be used. Particular interpolymerscontaining the diolefin are disclosed in U.S. Pat.No. 2,476,967.

Preferred interpolymers for use in the latex of the present inventionare the interpolymers containing a nitrogen compound having at least onereactive hydrogen attached to the nitrogen. Such interpolymers maycontain monovalent aminoesters, cyclic amines, and heterocyclic nitrogencompounds. These interpolymers are referred to herein as "aminoester"interpolymers and are aminoesters of unsaturated carboxylic acids suchas illustrated above. These interpolymers have outstanding adhesiontoward various substrates and exhibit outstanding solvent resistance.Such interpolymers are illustrated in U.S. Pat. Nos. 2,897,182;2,980,652; 3,261,797; and 3,261,799. This latter patent describespreparation of aminoester latices as such.

It is preferred, according to the present invention, to use an anionicsurfactant to improve the stability of the interpolymer latex,especially to improve shelf-life and wetting of the substrate by theformulated coating composition, although a non-ionic surfactant may beemployed. By shelf-life is meant the ability of the vehicle to be storedfor long periods of time without separation. A preferred anionicsurfactant is the sodium salt of dodecyldiphenylether sulfonate (forexample, Benax 2Al, a product of the Dow Chemical Company). Othersuitable surfactants are those stable in alkali media such as alkalisalts of acid phosphate esters of alcohols, phenols, ethoxylatedderivatives of alcohols, alkyl phenols and the like. The phosphateesters are commercially available as Gafac (a product of GeneralAniline).

A preferred vehicle of the present invention may be prepared byadjusting the alkali-lithium silicate solution and the stabilizedinterpolymer latex to approximately equal solids content and adding thesilicate solution to the latex under good mixing. Alternatively, diluentwater and stabilizing surfactant may be initially added to the latex,and the latex solution, adjusted to to about the same solids content asthe silicate solution, is then added to the alkali-lithium silicatesolution while stirring at high speed. Either method of preparationyields a vehicle having a long shelflife.

To the vehicles of the present invention is added zinc dust to formzinc-enriched coating compositions. The vehicles and zinc dust areformulated in accordance with the following general formula:

    ______________________________________                                                    Parts by Weight                                                               Optimum                                                           ______________________________________                                        Vehicle (26% NVM)                                                                           33        23.4      20                                          Zinc dust     67        76.6      80                                                                  100.0                                                 ______________________________________                                    

The coating compositions are described in terms of total weight. Thus,the vehicle when expressed as 26% NVM, means 26% non-volatile materialsor total solids.

The zinc has a particle size between 2 to about 50 microns in diameterand preferably the particles have a size within the range of 5 to 20microns in diameter. The zinc may be added in an amount from 66% toabout 80% by weight of the coating composition, and the coatingcompositions will impart increasing corrosion resistance to metal,especially carbon steel, as the amount of zinc is increased.

In addition to the composition previously discussed, certain othermaterials, generally referred to as pigments, may be added singly,collectively, or in various combinations to impart certain desiredproperties to the coating compositions. Several of these "pigmentadditives" and the desirable characteristics they provide are asfollows:

1. Inorganic ceramic pigments (metallic oxides which alone or in variouscombinations yield desired colors) -- Examples of the metallic oxidepigments are cobalt/aluminum, cobalt/chrome, cadmium, and cadmiumaluminum. The preferred pigments are those commonly used in tintingceramics.

2. Zinc oxide pigment -- Enhances the abrasion resistance and overall"smoothness" of the coating surface by contributing comparatively minute(0.1-1 micron diameter) particles to the coating formulation.

3. Aluminum silica-phosphate pigment -- Performs the same function aszinc oxide.

4. Titanium dioxide pigment -- In addition to enhancing the abrasionresistance of the coating, titanium dioxide contributes its excellenthiding properties (brought about by a very high index of refraction).

The coating compositions of the present invention may be applied tometal surfaces which have been prepared by commercial sandblastingtechniques or by wire brushing. The sandblasting need only to removeloose mill scale and rust, and need not be sandblasted to white metal asis required for the commercially available prior art zinc-rich inorganiccoating compositions. The coating compositions are applied to thesurface by brushing, rolling or spraying to obtain a dry film thicknessof about 1 to 12 mils in thickness. A preferred dry film thickness isabout 3 to 6 mils. To obtain the preferred dry film thickness, a wetfilm of about 6 to 10 mils of the coating composition is applied to thesurface.

The present invention will be further illustrated by the followingspecific examples which are given by way of illustration and not aslimitations on the scope of the present invention. Where precentages aregiven they are understood to be weight percents.

EXAMPLE I

A lithium-sodium silicate solution used in this invention without theaddition of any additive materials may be formed in the followingmanner:

Water, silica gel, lithium hydroxide, and sodium hydroxide are chargedinto a stainless steel pressure vessel equipped with an agitator. Duringthe initial mixing of these ingredients, evolution of heat raises thetemperature of the contents to 50° C. to 55° C. The reactor is thensealed and the temperature of the reactants, under a continual agitationis raised to 150° C. for a period of time, which may vary from 30 to 90minutes. After the vessel reaches about 150° C. and about 70 psipressure, the contents are slowly cooled at a rate of about 0.61° C. toabout 1.83° C. per minute. This will result in a temperature drop from150° C. to about 95° C. within about 30 to about 90 minutes. Thiscompletes the initial part of the reaction which forms the solidsodium-lithium silicates.

The second part of the operation (below 95° C.) requires a longer periodof time in order to effectively dissolve the solid silicates at thelower temperatures. The reduction of the temperature of the reactorcontents from 95° C. to 40° C. is at a rate of about 0.37° C. to 0.416°C. per minute and is accomplished in 150 minutes to 240 minutes. Thelast temperature drop from 40° C. to 25° C. may be conducted over aperiod of 60 to 120 minutes and a cooling rate of about 0.25° C. toabout 0.125° C. per minute.

Depending on the amount of water used, the vehicle may be used indifferent solid ratios, i.e. the total solids of the vehicle may varyfrom about 10% to 45% by weight, preferably the solids contents isbetween about 25% to about 30% by weight.

EXAMPLE 2

A vehicle was prepared in the manner similarly described in Example 1except it was made of the following ingredients:

    ______________________________________                                                          Parts by Weight                                             ______________________________________                                        Sodium Hydroxide    8                                                         Lithium Hydroxide Mono-hydrate                                                                    34                                                        Silica Gel          126                                                       Water               400                                                       ______________________________________                                    

This vehicle may be described as 0.25 Na₂ O : 0.75 Li₂ O : 4.5 SiO₂ orhaving a molar ratio of Li₂ O to Na₂ O of 3/1 and a molar ratio of SiO₂to the combined Li₂ O and Na₂ O of 4.5/1. The vehicle had a total solidscontent of about 27 weight percent but may vary between 26 to 28 weightpercent. The viscosity of the vehicle was 36 to 37 centerpoises, with aspecific gravity of about 1.194 to 1.195.

EXAMPLE 3

A vehicle of the present invention was prepared as follows:

    ______________________________________                                                           Parts by Weight                                            ______________________________________                                        Part A                                                                        Sodium-Lithium Silicate Solution of                                           Example 2            55.0                                                     Sodium Silicate Solution                                                      (1.0 Na.sub.2 O/3.22 SiO.sub.2) 37% Solids                                                         10.0                                                     Water                4.0                                                      Part B                                                                        Acrylic-Aminoester Latex*                                                     46% Solids           16.7                                                     Benax 2Al (26% Solids)                                                                             1.5                                                      Water                12.8                                                                          100.0                                                    ______________________________________                                         *Prepared according to U.S. Pat. No. 2,980,652                           

The acrylic-aminoester latex, in accordance with U.S. Pat. No.2,980,652, is prepared as disclosed from the monomer such as Formula VIdescribed in column 2 of U.S. Pat. No. 2,980,652 employing a peroxidecatalyst described in column 3, lines 65-71 and column 4, lines 31-45; anon-ionic or anionic surfactant as described also in column 4, lines7-14 and 60-70 is used. The acrylic reactant is disclosed in column 4,lines 70-75 and column 8, lines 6-70 of this patent. Theacrylic-aminoester latex so prepared (and used in this invention) is notheated but rather is used in the present invention without heating.Preparation of an acrylic aminoester latex as described involves use ofa small amount of surfactant (usually about 1-3% by weight) but thissmall amount employed in the preparation of the latex does notnecessarily obviate the use of additional surfactant as described aboveas Benax 2Al (26% solids). However, the total amount of surfactant inthe vehicle is quite small in that the amounts in the latex and thatadded to Part B are quite small and ordinarily does not exceed theamounts disclosed before. The surfactant does not significantly affectthe properties of the final coating.

The diluted stabilized latex (Part B) is added to the mixedsodium-lithium-silicate solution (Part A) which is at approximately thesame solids as the diluted latex. The addition is made slowly with goodagitation.

EXAMPLE 4

A vehicle was prepared similarly as in Example 3 wherein theacrylic-aminoester latex was Rhoplex AC-61, a product of Rohm & Haas.

EXAMPLE 5

An alternative procedure for making the vehicles of the presentinvention is as follows:

    ______________________________________                                                           Parts by Weight                                            ______________________________________                                        Acrylic-Aminoester Latex*                                                     46% Solids           16.7                                                     Water                16.8                                                     Benax 2al (26% Solids)                                                                             1.5                                                      Sodium Silicate Solution                                                      (1.0 Na.sub.2 O/3.22 SiO.sub.2) 37% Solids                                                         10.0                                                     Sodium-Lithium Silicate Solution                                              of Example 2         55.0                                                                          100.0                                                    ______________________________________                                         *Prepared according to U.S. Pat. No. 2,980,652                           

As described in Example 3 the ingredients are all added in the orderlisted above with good mixing.

EXAMPLE 6

Another composition in accordance with the present invention is made upas follows:

    ______________________________________                                                                Parts                                                                         by Weight                                             ______________________________________                                        Styrene/butadiene/itaconic acid                                               interpolymer (50% Total Solids)                                                                         15.4                                                Water                             29.1                                        Surfactant treated   Pre blend before                                          montmorilonite      adding to other                                                                            1.0                                         Benax 2Al (26% Solids)                                                                             ingredients  1.5                                         ______________________________________                                    

The ingredients are all added in the order listed above with goodmixing. The styrene/butadiene/itaconic acid interpolymer may contain60-70% styrene, 38-28% butadiene and 1-10% itaconic acid made byprocedures well known in the art of latex polymerization and containingfrom 0.5-3.0% anionic surfactant such as sodium laural sulfate or anonionic surfactant such as octyl phenoxypolyethoxy ethanol.

EXAMPLE 7

A vehicle using an interpolymer of styrene/butadiene/taconic acid latexhas been evaluated and also a zinc-containing composition. Salt fogexposures, solvent immersion tests, adhesion of coal tar epoxies,adhesion to nonsandblasted cold rolled steel, U.V. exposure ofunpigmented vehicle, film build studies at 50° F. and 75% RH and a fieldtest as well as 6 months ageing tests on this vehicle have all showndesirable results.

EXAMPLES 8-12

The following examples illustrate vehicles prepared by compoundingvarious organic interpolymers with alkali-lithium silicate solutionswhich may be used in the present invention. The various vehicles wereprepared to determine the stability at or about room temperature (77°F.). Each of the vehicles which are set forth in Table 1 hereinafterexhibit outstanding stability.

                                      TABLE I                                     __________________________________________________________________________    Example                  8    9    10   11   12                               __________________________________________________________________________    Sodium-lithium silicate solution                                              of Example 2 (26% solids)                                                                              55.8 55.8 55.8 55.8 55.8                             Sodium silicate solution ("N"  Sil)                                           (26% solids)             14.2 14.2 14.2 14.2 14.2                             Water (added to latex before blending)                                                                 12.7 12.7 12.7 14.4 13.7                             Interpolymer                                                                  Methyl methacrylate/butyl acrylate/                                           aminoester (Rhoplex AC-61, product                                            of Rohm & Haas) (46% solids)                                                                           17.3                                                 Styrene/acrylonitrile 2-ethylhexyl                                            acrylate (Ucar 680, a product of                                              Union Carbide) (45% solids)   17.3                                            Ethyl methacrylate/2-ethylhexylacrylate/                                      vinylacetate (Thoplex MV-1, a product of                                      Rohm & Haas) (46% solids)          17.3                                       Acrylonitrile/butadiene/styrene                                               (Hycar 1877X8, a product of B.F. Goodrich                                     (50% solids)                            15.6                                  Styrene butadiene (Dow 762W, a product of                                     Dow Chemical) (48% solids)                   16.3                             __________________________________________________________________________

EXAMPLES 13-17

To each of the vehicles of Examples 8-12 was added zinc dust to producea zinc-enriched coating composition. The coating compositions were madeup of about 23-24 parts by weight of the vehicle and about 76-77 partsby weight of zinc dust. The coating compositions were applied to Qpanels and then scribed to the bare metal. The panels were placed in asalt fog cabinet at 85° F. for 1500 hours. Each of the panels exhibitedexcellent protection to corrosion both at the scribes and overall.

Besides the foregoing coating compositions, systems were preparedcontaining various percentages of the organic interpolymer latex ascompared to the alkali-lithium silicate solution. It was found that whenthe interpolymer latex was between 10 to 40% of the coating compositionby weight on a solids basis a suitable zinc enriched coating could beproduced. While the ideal amount of the interpolymer required dependedto some degree on the specific nature of the latex it was found thatpreferably 15-30% of the interpolymer latex was the optimum to obtainmaximum corrosion protection.

The above coating compositions adhere to clean steel and will withstandextended immersion under running water after 24 hours. Salt fogexposures were run on sanded and sand-blasted steel panels for 1500hours. Corrosion protection was comparable to conventional zinc-richinorganic coating compositions. Normally, corrosion resistance isadversely affected by the addition of organic materials to inorganiccoatings. Solvent and abrasion resistance were also of the same order ofmagnitude as those of the zinc-rich inorganics. Other latices known tothe art do not exhibit good solvent resistance.

The following examples illustrate a vehicle and coating compositionwhere only sodium silicate is used.

EXAMPLE 18

A vehicle was made as follows:

    ______________________________________                                                           Parts by Weight                                            ______________________________________                                        Sodium Silicate Solution                                                      (37% Solids)         58.5                                                     Rhoplex AC-33 (A product of Rohm &                                            Haas) (46% Solids)   28.0                                                     Water (Distilled)    66.5                                                                          153.0                                                    ______________________________________                                    

The above vehicle separated into two phases, organic and inorganic,within 24 hours. The latex had a grainy appearance and after standingseveral weeks the top layer or organic phase formed a gel which was noteasily redispersed. Such a vehicle would be completely unsatisfactory asa commercial product due to its extremely short shelf-life.

EXAMPLE 19

A zinc-enriched coating composition was prepared using the vehicle ofExample 18 together with zinc dust as follows:

    ______________________________________                                                         Parts by Weight                                              ______________________________________                                        Vehicle of Example 18                                                                            23.4                                                       Zinc Dust          76.6                                                                          100.0                                                      ______________________________________                                    

The above zinc-rich coating composition was applied to sand-blastedsteel. After 24 hours the coating was placed under running water. Within15 minutes the coating had washed off to bare steel.

The foregoing examples 18 and 19 illustrate the importance of thelithium in the coating compositions of the present invention ascontrasted to the coating composition utilizing sodium silicate solutionalone. The compositions of this invention have extensive shelf-life,rapid attainment of water insensitivity, and impart outstandingcorrosion resistance when applied to a steel panel which has been merelycleaned well.

The nature and objects of the present invention having been completelydescribed and illustrated what we wish to claim as new and useful andsecure by Letters Patent is:
 1. A homogeneous vehicle for azinc-enriched, self-curing, water-resistant coating compositionconsisting essentially of:a. between about 57 to 91 parts of an aqueousalkali-lithium silicate solution, said alkali and lithium silicatesbeing employed in amounts sufficient to provide a molar ratio of X₂ O,where X is selected from the group consisting of sodium, potassium, andquaternary ammonium, to lithium oxide to silicon dioxide, respectively,within the range from about 0.25 to 0.65 X₂ O : 0.35 to 0.75 Li₂ O : 2.5to 4.5 SiO₂ ; b. between 9 and 40 parts of a film-forming organic alkalistable latex of an interpolymer selected from the group consisting ofinterpolymers of acrylonitrile/butadiene/styrene, ofstyrene/butadiene/maleic acid, of styrene/butadiene/itaconic acid and ofstyrene/butadiene; and c. between 0 and 3 parts of an alkali stableanionic surfactant.
 2. A vehicle according to claim 1 wherein theorganic alkali stable latex is a latex of an interpolymer ofacrylonitrile/butadiene/styrene.
 3. A vehicle according to claim 1wherein the organic alkali stable latex is a latex of an interpolymer ofstyrene/butadiene.
 4. A homogeneous vehicle for a zinc-enriched,self-curing, water-resistant coating composition consisting essentiallyof:a. between about 57 to 91 parts of an aqueous sodium-lithium silicatesolution, said sodium and lithium silicates being employed in amountssufficient to provide a molar ratio of sodium oxide (Na₂ O) to lithiumoxide (Li₂ O) to silicon dioxide, repsectively, within the range fromabout 0.25 to 0.65 Na₂ O : 0.35 to 0.75 Li₂ O : 2.5 to 4.5 SiO₂ ; b.between 9 and 40 parts a of film-forming organic alkali stable latex ofan interpolymer of styrene/butadiene/itaconic acid; and c. between 0 and3 parts of an alkali stable anionic surfactant.
 5. A coating whichcomprises 20 to 33 parts by weight of a vehicle of claim 1 wherein thelatex is a latex of an interpolymer of styrene/butadiene, and 67 to 80parts by weight of zinc dust.
 6. A coating composition in accordancewith claim 1 which comprises 20 to 33 parts by weight of a vehicle ofclaim 1, and 67 to 80 parts by weight of zinc dust.
 7. A coatingcomposition which comprises 20 to 33 parts by weight of a vehicle ofclaim 1 wherein the latex is a latex of an interpolymer ofstyrene/butadiene/acrylonitrile, and 67 to 80 parts by weight of zincdust.